Here's Something you might find Interesting
Posted: Mon 13 Jun, 2022 10:49 am
Have you ever wondered how you could make frames to look like these?
This is a little essay to examine some of the science involved in creating the same sort of finish on bare-wood mouldings.
We humans tend to favour a more aged look on our wooden frames and furniture. Even contemporary frames look a little better if they have a bit of history behind them.
Those who produce factory finished mouldings are aware of this and indeed share some of this knowledge.
So, let's first look first at what happens to a piece of wood if it is left exposed to daylight and air.
Wood has a cellular structure and we can see evidence of this when we soak some wood in water. If we shine a bright light onto the surface, it becomes translucent, absorbing the light and glowing with the natural colour of the wood species.
If the wood is now left to age over very many years, two important changes take place.
First the oils and tannins in the wood darken slightly due to their exposure to daylight.
But the second is the most important change.
Some of the cells on the surface of the wood oxidise and change from being translucent to becoming opaque. Now, instead of transmitting the light into the wood, some light is reflected back from the surface.
As an example, think of silvered oak. Look closely at it the next time. Behind that silvering you will find that the wood itself is quite dark and the silvering isn't that the surface has turned white, but that the oxidised surface has turned ash like and the light reflected off it is now 'scattered light'. Scattered light is white, the same as frosted glass appears white. If you wet this silvering, the whiteness disappears and changes colour to a dark brown.
Now we know that untreated wood will become silvery if left over time but the same wood if protected under a layer of French polish or wax, both of which are quite permeable, will create a slightly opaque surface which will reflect back some of the light as a particular shade of brown.
Here's an example of this.
The wood here is burr walnut and has been finished with a French polish.
With the light shining on it, we can see that the background wood grain shines with a golden yellow glow. But if we look closely, we can also see an overall brown cast which appears quite evenly spread across the surface. This is the aged oxidised layer that is slightly opaque and is reflecting back the light as a red/brown walnut colour. And this is the essence of the appearance of all antique furniture and frames.
Now let's see how we can reproduce that effect.
In the case where the wood has darkened, we add a wood stain, usually in the same shade as the timber and maybe adjust it a bit to look more antique.
On top of that stain, we now coat on what is called a 'colour glaze'. This a paint or varnish that has a small amount of earth pigment added and is stained to match the colour of the timber.
Here is a shade card of the most commonly used earth pigments for wood finishing.
They are called earth pigments because they are colours most closely related to those found in nature - rust browns. They never dissolve, ie are completely insoluble and opaque. They reflect back only their own colour. When added to any liquid, they will float around freely before settling back down on to the surface when that liquid evaporates.
Used on their own they are quite dull colours but can be livened up with a suitable transparent stain.
Over that colour glaze, we would add at least two coats of clear shellac varnish. This recreates that wetted effect which allows the light to penetrate the finishes and back into the wood.
Whilst a skilled French polisher can achieve a faultless finish on the top surface of the varnish, we can otherwise use two thin coats of bees-wax to complete the transparency of finish.
So, how do we make a colour glaze?
Well, I'll keep it simple and trust that anyone so interested will experiment and try it out for themselves. Make up a thinned shellac solution, ie 1 cap shellac to 2 caps meths. Stir in some dry powder spirit wood stain (E-bay), starting with Walnut then adding a bit of Mahogany, puddling it on to scrap wood until you have the colour that matches the finish you're aiming for.
Next strain the polish to remove any undissolved dye crystals.
Now add a small amount of Brown Umber pigment and repeat until the varnish you are puddling turns from crystal clear to slightly opaque - ie, it should now have some 'body'. You can only do this by trial and error.
I've chosen Brown Umber because it is quite an old 'English' colour, reminiscent of the BBC and wooden wireless sets from the fifties.
Paint two coats of the colour varnish over the stained wood and leave to dry. You must use a soft bristle brush or mop to avoid streaking.
To finish, paint on two coats of transparent polish. Make sure to de-nib between coats.
I hope that by reading this some might look again at antique frames and now understand why they look the way they do and how with some practice and the correct materials, anyone can reproduce that appearance for their own work.
This is a little essay to examine some of the science involved in creating the same sort of finish on bare-wood mouldings.
We humans tend to favour a more aged look on our wooden frames and furniture. Even contemporary frames look a little better if they have a bit of history behind them.
Those who produce factory finished mouldings are aware of this and indeed share some of this knowledge.
So, let's first look first at what happens to a piece of wood if it is left exposed to daylight and air.
Wood has a cellular structure and we can see evidence of this when we soak some wood in water. If we shine a bright light onto the surface, it becomes translucent, absorbing the light and glowing with the natural colour of the wood species.
If the wood is now left to age over very many years, two important changes take place.
First the oils and tannins in the wood darken slightly due to their exposure to daylight.
But the second is the most important change.
Some of the cells on the surface of the wood oxidise and change from being translucent to becoming opaque. Now, instead of transmitting the light into the wood, some light is reflected back from the surface.
As an example, think of silvered oak. Look closely at it the next time. Behind that silvering you will find that the wood itself is quite dark and the silvering isn't that the surface has turned white, but that the oxidised surface has turned ash like and the light reflected off it is now 'scattered light'. Scattered light is white, the same as frosted glass appears white. If you wet this silvering, the whiteness disappears and changes colour to a dark brown.
Now we know that untreated wood will become silvery if left over time but the same wood if protected under a layer of French polish or wax, both of which are quite permeable, will create a slightly opaque surface which will reflect back some of the light as a particular shade of brown.
Here's an example of this.
The wood here is burr walnut and has been finished with a French polish.
With the light shining on it, we can see that the background wood grain shines with a golden yellow glow. But if we look closely, we can also see an overall brown cast which appears quite evenly spread across the surface. This is the aged oxidised layer that is slightly opaque and is reflecting back the light as a red/brown walnut colour. And this is the essence of the appearance of all antique furniture and frames.
Now let's see how we can reproduce that effect.
In the case where the wood has darkened, we add a wood stain, usually in the same shade as the timber and maybe adjust it a bit to look more antique.
On top of that stain, we now coat on what is called a 'colour glaze'. This a paint or varnish that has a small amount of earth pigment added and is stained to match the colour of the timber.
Here is a shade card of the most commonly used earth pigments for wood finishing.
They are called earth pigments because they are colours most closely related to those found in nature - rust browns. They never dissolve, ie are completely insoluble and opaque. They reflect back only their own colour. When added to any liquid, they will float around freely before settling back down on to the surface when that liquid evaporates.
Used on their own they are quite dull colours but can be livened up with a suitable transparent stain.
Over that colour glaze, we would add at least two coats of clear shellac varnish. This recreates that wetted effect which allows the light to penetrate the finishes and back into the wood.
Whilst a skilled French polisher can achieve a faultless finish on the top surface of the varnish, we can otherwise use two thin coats of bees-wax to complete the transparency of finish.
So, how do we make a colour glaze?
Well, I'll keep it simple and trust that anyone so interested will experiment and try it out for themselves. Make up a thinned shellac solution, ie 1 cap shellac to 2 caps meths. Stir in some dry powder spirit wood stain (E-bay), starting with Walnut then adding a bit of Mahogany, puddling it on to scrap wood until you have the colour that matches the finish you're aiming for.
Next strain the polish to remove any undissolved dye crystals.
Now add a small amount of Brown Umber pigment and repeat until the varnish you are puddling turns from crystal clear to slightly opaque - ie, it should now have some 'body'. You can only do this by trial and error.
I've chosen Brown Umber because it is quite an old 'English' colour, reminiscent of the BBC and wooden wireless sets from the fifties.
Paint two coats of the colour varnish over the stained wood and leave to dry. You must use a soft bristle brush or mop to avoid streaking.
To finish, paint on two coats of transparent polish. Make sure to de-nib between coats.
I hope that by reading this some might look again at antique frames and now understand why they look the way they do and how with some practice and the correct materials, anyone can reproduce that appearance for their own work.